1. Field of the Invention
The present invention relates generally to electronic identification and recognition systems and more specifically to an electronic identification and recognition system wherein the identifier incorporates a code changeable reactance.
2. Description of the Prior Art
There are various electronic identifying systems wherein the identifier may be in the form of an electronically passive card-type structure. For example, U.S. Pat. No. 3,752,960 entitled "Electronic Identification and Recognition System", granted to the current inventor; U.S. Pat. No. 4,223,830 entitled "Personal Identification and Signaling System", granted to the current inventor; and U.S. Pat. No. 4,196,418 entitled "Detection Plate for an Identification System", granted to Harm J. Kip are illustrative. The U.S. Pat. No. 3,752,960 uses a simple card circuit but has the disadvantage of a limited number of codes and some loss of detection range due to the fact that only one half or one quarter of the card is dedicated to the inductive pick-up loop. U.S. Pat. No. 4,223,830 may incorporate numerous codes but has a disadvantage of requiring a separate power source. The U.S. Pat. No. 4,196,418 has a disadvantage of not being resonant for portions of its cycle and therefore unable to send or receive a positive radiated signal when in the damped or detuned mode, nor is its receiver portion capable of measuring the frequency of the identifier card, nor can additional information be sent through choice of a second radio frequency.
U.S. patent application Ser. No. 221,720, by the present inventor, filed Dec. 31, 1980, refers to a radio frequency emitting identifier which uses a single radio frequency and requires lengthy transmission time. U.S. patent application Ser. No. 264,856, by the present inventor, used two frequencies but requires two oscillators in the identification element and does not have a code switchable reactance.